1. Field of the Invention
The present invention relates to a printing technique for printing by means of ejecting ink droplets.
2. Description of the Related Art
Ink jet printers, which eject ink from a head, have come to enjoy widespread use as computer output devices in recent years. While conventional ink-jet type printers can only reproduce xe2x80x9cbilevelxe2x80x9d (i.e. On or Off) pixels, more recently there have been developed multilevel printers that can reproduce individual pixels at three or more gradation levels. Multilevel pixels can be reproduced, for example, by adjusting the size of the dot produced at each pixel location. To produce dots having a plurality of different sizes, a drive signal having a complex waveform for selectively ejecting different volumes of ink is used. The volume of ink ejected at each pixel location is adjusted by shaping the drive signal.
However, where a single type of drive signal is used, the volume of ink ejected per pixel can only be varied by about three levels at most. This imposes limitations on local gradation reproduction for each pixel. In other words, there is a rather small degree of freedom as regards local gradation reproduction through adjustment of the volume of ink ejected for each pixel. If the degree of freedom in local gradation reproduction could be increased, it would be possible to achieve higher print quality and faster printing. Accordingly, for some time there has been a need for a technique to increase the degree of freedom in local gradation reproduction.
Accordingly, an object of the present invention is to provide increased degree of freedom in local gradation reproduction, thereby attaining higher print quality or faster printing speed.
In order to attain at least part of the above and other related objects of the present invention, there is provided a printing device for printing on a print medium while performing main scanning. The printing device comprises: a print head having a plurality of nozzles ejecting a same given ink and a plurality of eject drive elements for causing droplets of ink to be ejected from the plurality of nozzles; a main scan drive section for performing main scanning by means of moving the print medium and/or the print head; a sub scan drive section performing sub scanning by means of moving the print medium and/or the print head; a head drive section for providing a drive signal to each eject drive element in response to a print signal; and a controller for controlling the sections; the controller having a first print mode. The gradation reproduction with the same ink is performed by: (i) designating as a unit of gradation reproduction a group of N contiguous pixels arranged in a selected one of a main scan direction and a sub scan direction where N is an integer of at lease 2; (ii) setting a volume of ink ejectable onto at least one pixel location of the N pixels to a value different from a volume of ink ejectable onto other pixel locations; and (iii) controlling the volume of ink at each pixel location of the N pixels to reproduce M gradation levels for each group of the N pixels where M is an integer of at least N+2.
This printing device uses N contiguous pixels in a given direction as a unit for gradation reproduction to reproduce M (Mxe2x89xa72) gradation levels, thereby providing a high degree of freedom as to the volume of ink ejected onto the N pixels. The printing device can attain improved gradation reproduction accordingly.
The present invention is also directed to a dot placement adjustment method for the printing device. The method comprises the steps of: (a) printing a first test pattern including two dot types of different size such that the two dot types are recorded substantially arrayed in single columns in the sub scanning direction; (b) determining a relative correction value for placement in the main scanning direction for the two dot types with reference to the first test pattern; and (c) performing correction of relative position of the two dot types using the relative correction value during printing, while forming the two dot types at different pixel locations on a same main scan line.
According to this method, ink droplets containing mutually different volumes of ink are used to record a plurality of dot types having different size at different pixel locations in the main scanning direction, so that placement adjustment can be performed so as the adjust the positions of the dots in the main scanning direction.
The second embodiment of the present invention is premised on controlling a printing device equipped with a plurality of nozzles capable of performing high-resolution printing by ejecting individual ink drops onto each pixel. Low-resolution image data are generated based on high-resolution image data when the print control device outputs printing data to the printing device. The low-resolution image data are created by assuming that each group of high-resolution pixels adjacent to each other constitute one low-resolution pixel. The low-resolution image data are used to eject ink drops onto each high-resolution pixel.
Specifically, nozzles traditionally eject ink drops onto each high-resolution pixel according to high-resolution image data, but if the nozzle resolution, or the nozzle pitch, does not correspond to the high resolution, a plural scan passes are required to complete printing on each row of high-resolution pixels. The use of low-resolution image data in the second embodiment of the present invention, on the other hand, reduces the number of scan passes required to complete dot formation on each row of high-resolution pixels. For example, low-resolution image data is prepared to represent dot formation state for each low-resolution pixel which includes two high-resolution pixels. In this case, two neighboring nozzles will eject ink drops onto two neighboring high-resolution pixels according to the low-resolution image data for a single low-resolution pixel corresponding to the two high-resolution pixels.
The invention may take a number of different embodiments, examples being a printing method and printing device; a printing control method and printing control device; a method and device for correcting dot placement; a computer program for realizing the functions of these methods and devices; a storage medium storing such a computer program; a data signal containing the computer program, applied to a carrier wave; and so on.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with the accompanying drawings.